Thousands of U.S.-employed private military personnel have become vulnerable to unconventional warfare attacks in Iraq.

Industry sources and analysts said private military and security contractors, particularly those employed by the Coalition Provisional Authority, have come under attack by Saddam loyalists and Al Qaida-inspired insurgents in the Sunni Triangle. They said that unlike the U.S. Army, these contractors have been helpless against such insurgency weapons as rocket-propelled grenades, mortars and roadside bombs.

Iraq has served as the first test of a U.S. Defense Department policy to hire private military and security firms to compensate for the shortfall in coalition troops. The analysts said that for the first time private companies have been conducting missions that until 2003 were the responsibility of U.S. combat troops, Middle East Newsline reported. So far, they said, more than 15,000 private security guards have been deployed in Iraq.

"The contractors that are reporting on what's going on are saying that, 'Look, this is a tough situation. It's very dangerous. There's people sniping at us every day,'" said Peter Singer, a senior fellow at the Washington-based Brookings Institution and author of a book on the private military industry. "They're facing far greater threats than U.S. forces do. And that's a major challenge here."

On Wednesday, Sunni insurgents attacked a convoy of a U.S.-based military company in Faluja. Four U.S. nationals were killed and a mob dragged their bodies through the streets of the city before hanging them on a bridge over the Euphrates River.

U.S. officials have pledged that the military will return to pacify Faluja. But they said such an operation would not be immediate.

"It's going to be deliberate. It will be precise. And it will be overwhelming," U.S. Army Brig. Gen. Mark Kimmitt, deputy operations director of coalition forces, said on Thursday. "The coalition is stepping up its offensive tempo to kill or capture anti- coalition elements and enemies of the Iraqi people, in response to the latest increase in violence."

Kimmit said the U.S. military has not returned to Faluja and advised foreigners to avoid entering the city. He said this advisory would not last long.

About 30 private security personnel have been killed in Iraq since May 2003, industry sources said. The Defense Department does not release data on casualties among private security personnel.

The private military personnel killed in Faluja were staffers from the North Carolina-based Blackwater USA, with 300 employees in Iraq, most of them ex-U.S. special operations force members. One of the company's missions has been to guard food convoys in the Faluja area.

"The graphic images of the unprovoked attack and subsequent heinous mistreatment of our friends exhibits the extraordinary conditions under which we voluntarily work to bring freedom and democracy to the Iraqi people," Blackwater said in a statement.

Blackwater, regarded as one of the most prominent U.S. military contractors in Iraq, has also been protecting CPA administrator Paul Bremer as well as U.S. government convoys and oil facilities. Over the last six months, the company has recruited ex-commandos from South Africa and South America.

"We do have a contract with Blackwater relating to Ambassador Bremer's security," CPA senior adviser Dan Senor said. "They are involved with protecting Ambassador Bremer. They are, obviously, not the only institution that is involved with his security."

Halliburton has been identified as the prime contractor of military and security personnel in Iraq. The company, offering annual tax-free salaries of up to $100,00, has also been recruiting Americans to work as construction workers, truck drivers and cooks. Employees from non-Western countries have been offered about half that amount.

Another major military contractor to have emerged in Baghdad was Global Risks. The British firm, the sixth largest foreign military firm in Iraq, was said to have employed 100 ex-British SAS commandos as well as 500 former Nepalese and Fiji soldiers.

Industry sources said up to15 percent of the $18.1 billion in U.S.-financed reconstruction projects in Iraq has been allocated to security, including training, weaponry and protection for the CPA. They said the number of security guards in Iraq has been rapidly increasing in an attempt to facilitate reconstruction projects amid the Sunni insurgency war.

"So it's a fact of life that not only are men and women in uniform dying, but you're having security people dying in significant numbers and most are ex-U.S. military," Anthony Cordesman, a former senior Pentagon official who is also with Brookings, said.